An approach to modal analysis of power system angle stability

An approach to modal analysis and modal identification is proposed, capable of complementing the panoply of existing methods. It is based on a hybrid time-domain – direct transient stability method called SIME (for SIngle Machine Equivalent). In short, SIME uses a conventional transient stability program to transform the time varying parameters of the system into those of a one-machine infinite bus (OMIB) equivalent system. The representations of this OMIB allow substantial reduction of the original problem’s dimensionality. Many important advantages may result. For example, the multimachine system unstable equilibrium point (UEP) can readily be derived from the OMIB UEP, which is calculated analytically and unambiguously in a two-dimensional space. Further, the interplay between multimachine and OMIB characteristics and their complementary properties provides a better understanding and handling of damping, inter-area oscillations and their control. More generally, modal analysis and modal identification tasks get closer to each other and easier to handle. The paper essentially focuses on the approach as such rather than on potential applications. Simulations carried out on a 3-machine system illustrate main features.